Add an option to force compiling object file output

Add an option to skip module hash checking that checks if swift compiler can
skip object file generation because it is going to produce the same
result. Always generation object file output when flag is used so we can
check for output determinism.

Author: cachemeifyoucan

include/swift/AST/IRGenOptions.h

@@ -315,6 +315,9 @@ class IRGenOptions {
   /// Print the LLVM inline tree at the end of the LLVM pass pipeline.
   unsigned PrintInlineTree : 1;
 
+  /// Always recompile the output even the module hash might match.
+  unsigned AlwaysCompile : 1;
+
   /// Whether we should embed the bitcode file.
   IRGenEmbedMode EmbedMode : 2;
 
@@ -472,7 +475,7 @@ class IRGenOptions {
         DisableLLVMOptzns(false), DisableSwiftSpecificLLVMOptzns(false),
         Playground(false),
         EmitStackPromotionChecks(false), UseSingleModuleLLVMEmission(false),
-        FunctionSections(false), PrintInlineTree(false),
+        FunctionSections(false), PrintInlineTree(false), AlwaysCompile(false),
         EmbedMode(IRGenEmbedMode::None), LLVMLTOKind(IRGenLLVMLTOKind::None),
         SwiftAsyncFramePointer(SwiftAsyncFramePointerKind::Auto),
         HasValueNamesSetting(false), ValueNames(false),

include/swift/Option/FrontendOptions.td

@@ -1138,6 +1138,9 @@ def enable_emit_generic_class_ro_t_list :
 def enable_swift_deterministic_check :
   Flag<["-"], "enable-swift-deterministic-check">,
   HelpText<"Check swift compiler output determinisim by run it twice">;
+def always_compile_output_files :
+  Flag<["-"], "always-compile-output-files">,
+  HelpText<"Always compile output files even it might not change the results">;
 
 def experimental_spi_only_imports :
   Flag<["-"], "experimental-spi-only-imports">,

lib/Frontend/CompilerInvocation.cpp

@@ -2191,6 +2191,7 @@ static bool ParseIRGenArgs(IRGenOptions &Opts, ArgList &Args,
   Opts.UseProfile = ProfileUse ? ProfileUse->getValue() : "";
 
   Opts.PrintInlineTree |= Args.hasArg(OPT_print_llvm_inline_tree);
+  Opts.AlwaysCompile |= Args.hasArg(OPT_always_compile_output_files);
 
   Opts.EnableDynamicReplacementChaining |=
       Args.hasArg(OPT_enable_dynamic_replacement_chaining);

lib/IRGen/IRGen.cpp

@@ -743,7 +743,7 @@ bool swift::performLLVM(const IRGenOptions &Opts,
     ArrayRef<uint8_t> HashData(reinterpret_cast<uint8_t *>(&hash),
                                sizeof(hash));
     if (Opts.OutputKind == IRGenOutputKind::ObjectFile &&
-        !Opts.PrintInlineTree &&
+        !Opts.PrintInlineTree && !Opts.AlwaysCompile &&
         !needsRecompile(OutputFilename, HashData, HashGlobal, DiagMutex)) {
       // The llvm IR did not change. We don't need to re-create the object file.
       return false;

test/Frontend/output_determinism_check.swift

@@ -3,10 +3,14 @@
 // RUN: %target-swift-frontend -module-name test -emit-sib -o %t/test.sib -primary-file %s -enable-swift-deterministic-check 2>&1 | %FileCheck %s --check-prefix=SIB_OUTPUT
 
 /// object files are "not" deterministic because the second run going to match the mod hash and skip code generation.
-// RUN: not %target-swift-frontend -module-name test -c -o %t/test.o -primary-file %s -enable-swift-deterministic-check 2>&1 | %FileCheck %s --check-prefix=OBJECT_OUTPUT
+// RUN: not %target-swift-frontend -module-name test -c -o %t/test.o -primary-file %s -enable-swift-deterministic-check 2>&1 | %FileCheck %s --check-prefix=OBJECT_MISMATCH
+/// object files should match when forcing object generation.
+// RUN: %target-swift-frontend -module-name test -c -o %t/test.o -primary-file %s -enable-swift-deterministic-check -always-compile-output-files 2>&1 | %FileCheck %s --check-prefix=OBJECT_OUTPUT
 
 // MODULE_OUTPUT: remark: produced matching output file '{{.*}}{{/|\\}}test.swiftmodule'
 // SIB_OUTPUT: remark: produced matching output file '{{.*}}{{/|\\}}test.sib'
-// OBJECT_OUTPUT: error: output file '{{.*}}{{/|\\}}test.o' is missing from second run
+// OBJECT_OUTPUT: remark: produced matching output file '{{.*}}{{/|\\}}test.o'
+// OBJECT_MISMATCH: error: output file '{{.*}}{{/|\\}}test.o' is missing from second run
 
 public var x = 1
+public func test() {}